Summary of Significant Accounting Policies - Additional Information (Details)	3 Months Ended		12 Months Ended
	Dec. 31, 2018 USD ($)	Jun. 30, 2018 USD ($)	Dec. 31, 2019 USD ($) reporting_unit	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 reporting_unit	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Jan. 01, 2019 USD ($)	Jan. 01, 2018 USD ($)	Jan. 01, 2017 USD ($)
Summary Of Significant Accounting Policies [Line Items]
Number of reporting units | reporting_unit			7			7
Segment allocation, goodwill recognized	$ 4,500,000,000		$ 4,493,000,000	$ 4,500,000,000	$ 4,535,000,000
Minimum percentage of estimated fair value of reporting unit to be less than carrying amount of goodwill			50.00%
Percentage of fair value in excess of carrying amount			50.00%
Impairment of goodwill (A and N)			$ 0	0	$ 719,000,000
Period required for impairment testing of reporting units			3 years
Businesses expected to be disposed within, years			1 year
Right-of-use assets			$ 252,000,000							$ 320,000,000
Revenue, terms of payment, period			30 days
Cash proceed from Other noncurrent liabilities										119,000,000
Properties, plants, and equipment, net	5,704,000,000		$ 5,463,000,000	5,704,000,000						24,000,000
Cash proceeds from Other noncurrent assets	416,000,000		514,000,000	416,000,000						22,000,000
Cumulative effect adjustment										73,000,000	$ 0	$ 0
Amount of stranded tax effects in accumulated other comprehensive income reclassified to accumulated deficit	367,000,000
Engineered Products and Forgings
Summary Of Significant Accounting Policies [Line Items]
Number of reporting units | reporting_unit						4
Segment allocation, goodwill recognized	4,186,000,000		4,067,000,000	4,186,000,000			$ 7,000,000
Impairment of goodwill (A and N)				719,000,000
Engineered Products and Forgings | Alcoa Forging and Extrusions
Summary Of Significant Accounting Policies [Line Items]
Impairment of goodwill (A and N)				719,000,000
Transportation and Construction Solutions
Summary Of Significant Accounting Policies [Line Items]
Number of reporting units | reporting_unit						3
Global Rolled Products
Summary Of Significant Accounting Policies [Line Items]
Segment allocation, goodwill recognized	$ 314,000,000		$ 426,000,000	$ 314,000,000			$ 68,000,000
Minimum | Engineered Products and Forgings
Summary Of Significant Accounting Policies [Line Items]
Percentage of total goodwill allocated to two reporting units			90.00%
Aluminum extrusions
Summary Of Significant Accounting Policies [Line Items]
Segment allocation, goodwill recognized									$ 110,000,000
Engine products
Summary Of Significant Accounting Policies [Line Items]
Segment allocation, goodwill recognized								$ 105,000,000
Arconic Engines
Summary Of Significant Accounting Policies [Line Items]
Segment allocation, goodwill recognized			$ 2,164,000,000
Percentage of fair value in excess of carrying amount		13.00%
Fastening systems
Summary Of Significant Accounting Policies [Line Items]
Segment allocation, goodwill recognized			1,607,000,000
Arconic Engineered Structures
Summary Of Significant Accounting Policies [Line Items]
Segment allocation, goodwill recognized			289,000,000
Forged wheels
Summary Of Significant Accounting Policies [Line Items]
Segment allocation, goodwill recognized			$ 7,000,000
Disks Asset Group
Summary Of Significant Accounting Policies [Line Items]
Impairment of goodwill (A and N)		$ 0
ASU 2017-12
Summary Of Significant Accounting Policies [Line Items]
Cumulative effect adjustment										$ 2,000,000